1. Field of the Invention
The present invention relates to a connecting structure of a branch connector formed of a branch pipe or a joint fixture in a cylindrical fuel pressure accumulating container or a spherical fuel pressure accumulating container such as a high-pressure fuel manifold and a high-pressure fuel block, and, more specifically, to a connecting structure of a branch connector in a fuel pressure accumulating container for supplying a high-pressure fuel not less than 1000 kgf/cm2 in a diesel internal combustion engine.
2. Description of the Related Art
The cylindrical fuel pressure accumulating container having a cylindrical inner peripheral wall surface includes an cylindrical container 111 having a flow path 111-1 therein, which corresponds to the cylindrical fuel pressure container, and branch pipes 112, which corresponds to the branch connector, connected to the cylindrical container 111 directly or via a joint fixture or the like as shown in FIG. 22 as an example. On the other hand, the spherical fuel pressure accumulating container having at least partly a spherical inner peripheral wall surface includes a spherical container 121 having a spherical space 121-1 therein, which corresponds to the spherical fuel container, and the branch pipe 112, which corresponds to the branch connector, connected to the spherical container 121 directly or via a joint fixture or the like as shown in FIG. 23 as an example. The structure of the spherical container 121 is such that, as shown in the figure, an upper half body 121a and a lower half body 121b having semi-spherical recesses respectively therein are fixedly connected by a bolt 121c. Reference numeral 121d designates a sealing packing.
The connecting structure of the branch connector in the cylindrical fuel pressure accumulating container shown in FIG. 22 includes a connecting structure in which a connecting end 112-1 of the branch pipe 112, which has the same diameter as the branch pipe 112 itself, is joined (by means of brazing or the like) with through holes 111-2 communicated with the flow path formed on the peripheral wall of the cylindrical container 111 in a state of being fitted therein, and a structure in which the connecting end 114-1 of the branch joint fixture 114 is joined (by means of brazing or the like) with through hole 111-2 in a state of being inserted therein, and the branch pipe 112 is connected to branch joint fixture 114 by a nut 115 as shown in FIG. 24.
The connecting structure of the branch connector in the spherical fuel pressure accumulating container shown in FIG. 23 includes a connecting structure in which the connecting end 112-1 of the branch pipe 112, which has the same diameter as the branch pipe 112 itself, is joined (by means of brazing or the like) with through holes 121-2 communicated with the space 121-1 formed on the peripheral wall of the spherical container 121 in a state of being fitted therein, and a structure in which the connecting end 114-1 of the branch joint fixture 114 is joined (by means of brazing or the like) with the through hole 121-2, as shown in FIG. 25 in a state of being fitted therein, and the branch pipe 112 is connected to branch joint fixture 114 by a nut 115.
In the case of the connecting structure of the branch connector in the cylindrical fuel pressure accumulating container, the distal end of the branch pipe 112 or the branch joint fixture 114 may be fitted into and joined with the through hole 111-2 in such a manner that the branch pipe 112 or the branch joint fixture 114 is fitted so that the outer peripheral edge 112a or 114a of the branch pipe 112 or the branch joint fixture 114 comes into contact with the inner wall of the through hole 111-2 and a recess 111-3 is formed at the opening of the through hole 111-2.
However, in such connecting structure, a large stress is generated at the opening end P of the branch connector, such as the branch pipe 112 and the branch joint fixture 114 communicating with the pressure accumulating container, due to constantly repeated abrupt variations in supplied pressure of the high-pressure fluid not less than 1000 kgf/cm2, and, especially variations in relative dimensions between the mating members (mating bearing surfaces) due to vibrations applied by an engine and increase and decrease of ambient temperature, and thus it is susceptible to cracking originating from the opening end P, which may results in leakage of fuel or the like from time to time. In the case of the cylindrical fuel pressure accumulating container, as shown in FIG. 22B, a large stress is generated at two opening ends P aligned in the axial direction.
Therefore, the following countermeasures are generally taken. In order to increase fatigue strength at the opening end of the branch connector communicating with the pressure accumulating container due to internal pressure, a method of employing a high-strength steel, there are a method, of increasing the strength of material by heat treatment including carbonitriding and the like, a method of employing a forged type or an assembled type (eye-joint type) as a pressure accumulating container, and so on.
However, with the method of employing high-strength steel as a branch connector such as the branch pipe and the joint fixture, there is a problem in durability since the high-strength steel is very hard to weld, and cannot be hardened. by heat processing. With the method of enhancing the strength of material by heat treatment including carbonitriding and the like, there is a drawback in that the strength cannot be enhanced because brazing filler metal of the brazed article is deteriorated by heat treatment in a furnace, and thus it is intolerable to be used in a high-pressure application. In addition, the forged type or the assembled type is disadvantageously heavy in weight and expensive.
In view of the problems of the related art described above, the invention provides a connecting structure of the branch connector in the fuel pressure accumulating container capable of increasing the internal pressure fatigue strength by lowering the maximum stress value generated at the inner periphery of the lower end of the branch connector such as the branch pipe and the joint fixture.